The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Selective catalytic reduction (SCR) catalysts and diesel oxidation catalysts (DOC) are commonly used with diesel engines for emissions reduction. In the SCR process, NOx reacts with a reductant which is injected by a dosing system into the flue or exhaust gas stream to be absorbed onto a SCR catalyst. The injected dosing agent (e.g. urea) breaks down to form ammonia (NH3), which is the reductant utilized to react with the NOx producing nitrogen (N2) and water (H2O).
However, the SCR process typically requires relatively high exhaust gas temperatures, such as temperatures greater than 220° C. In conventional diesel applications, relatively low exhaust gas temperatures, such as temperatures less than 220° C., can be experienced frequently. Therefore, external heating devices may be used to maintain SCR catalyst temperatures during periods of low exhaust gas temperature.